This is an interactive proposal from radiation oncologists, urologists, radiologists and medical physicists at the University of Maryland investigating the use of Magnetic Resonance Spectroscopic Imaging (MRSI) to guide the delivery of radiation during prostate brachytherapy (PB). MRSI provides biochemical information on the levels of citrate and choline in the prostate to localize the cancer within the gland. Previous work at University of Maryland established relationship of citrate metabolism in prostate cancer and the molecular events that are characteristic in the malignant transformation. The ability to image the chemical makeup of the prostate with MRSI has become feasible during the last few years, but whether this information can be used effectively to treat prostate cancer patients with radiation is unknown. In order to explore the hypothesis that MRSI can be used to improve PB treatment, the following 3 specific aims will be explored: Specific aim 1 will test the hypothesis that MRSI information can be effectively incorporated into the treatment planning of prostate brachytherapy. Specific aim 2 will test the hypothesis that a pilot study and a Phase II trial utilizing MRSI-Guided prostate brachytherapy can be performed safely and effectively. Specific aim 3 will test the hypothesis that MRSI can provide a unique assessment of treatment response after radiation therapy to the prostate gland. We have conducted preliminary pilot work using MRSI in PB, which is encouraging. Our basic scientists in our physics division have strong backgrounds in this area and have worked closely with clinicians in translating the MRSI information into the therapy of our patients with prostate cancer.